This invention relates generally to techniques for maintaining the orbits of earth-orbiting satellites and, more specifically, to techniques for maintaining such satellites in relatively low-altitude, nearly circular orbits. Some applications of satellite communications require the launching and maintenance of many satellites in low earth orbits.
The principal difficulty in maintaining a low earth orbit is that it is continuously degraded by atmospheric drag. The conventional process for overcoming drag involves tracking the satellite from the ground, determining the commands needed to raise the orbit, transmitting these commands to the satellite, and executing the commands on the satellite to effect a desired orbital correction. Because of the high cost and potential for error in this communication and computation process, orbital correct ion maneuvers are typically scheduled as infrequently as possible. As a result, orbit maintenance is not always performed in a most fuel-efficient manner, and the potential life of the satellite is not as long as it might be. Further, the total cost of maintaining a large constellation of satellites by this technique is prohibitively high for many applications.
Ideally, what is needed is a system for making orbital corrections on a more frequent and reliable basis, without the high cost and potential for catastrophic errors associated with ground-based control. The present invention satisfies this need.